Technical Field
The present invention relates to a method of removing wastewater contained in a water retention tank of a grey-water management system for an aircraft toilet, and it also relates to a grey-water management system for managing the grey water of an aircraft.
Description of the Related Art
In particular in the field of aviation, it is well known to use “vacuum” toilets to flush waste into a septic tank. The water used in such vacuum toilets generally comes from grey water in turn coming from the washbasins or from the galley of the aircraft, so as to limit the quantity of water taken on board, and, ultimately, so as to limit the weight of the aircraft. The “galley” of an aircraft is the special compartment from which the meals are served. The term “grey water” means wastewater that does not contain much pollutant matter, such as wastewater of domestic origin resulting from washing dishes or hands, in particular.
Thus, the grey-water management system usually includes a washbasin, a water supply faucet or tap for supplying water to said washbasin, a drain for draining wastewater from the washbasin, which drain is connected to a retention tank provided with a filter, and a bowl or pan supplied with water by a pump connected to the retention tank. The system generally also includes a main wastewater tank, the bowl and the retention tank being connected to said main tank via pipes that are respectively equipped with a valve and with a solenoid valve.
The pumps used in such grey-water management systems consist of “rotodynamic” pumps, such as, for example, centrifugal pumps and/or positive displacement pumps, powered by electrical energy or by hydraulic energy.
The rotodynamic pumps that are in most widespread use in grey-water management systems are centrifugal pumps or turbine pumps, such a pump including a pump body constituted mainly of a suction or inlet pipe, of a volute chamber or casing, and of a delivery or discharge pipe. The volute chamber receives the moving portion or rotor that is formed by an impeller, said impeller being in the form of a bladed wheel mounted on a shaft. The rotor is actuated by a drive machine that may be an electric motor, a hydraulic motor, an internal combustion engine, or a turbine.
That type of pump suffer from numerous drawbacks. Generally, that type of pump suffers from having poor energy efficiency, which lies approximately in the range 30% to 70%, from having a large overall volume and a large overall weight, from having considerable wear on the rotating parts, requiring frequent maintenance, and from being sensitive to the phenomenon of cavitation. Cavitation is a noisy phenomenon that can destroy a machine in a few minutes. During the pumping, the liquid situated inside a centrifugal pump does not have a uniform pressure. In particular, zones are present in it that have suction or negative pressure that is accentuated to various extents. When the pumped liquid is sufficiently close to its boiling point, i.e., to the point at which it goes from the liquid state to the gas state, it can happen that the pressure at those points falls below its vapor pressure, so that vapor bubbles are formed in the pump. When such bubbles reach the zones in which the pressure is going back up, they implode suddenly. The implosion is accompanied by noise, and, when it takes place in the vicinity of a wall, it can cause mechanical damage by causing micro-perforations in the metal (erosion).
The other pumps that are used in grey-water management systems are Venturi pumps. Unfortunately, such pumps that use the Venturi effect require another type of pump to be used to generate the drive pressure, thereby increasing the overall weight. In addition, such pumps have very low energy efficiency, of in the range 10% to 25%, and are sensitive to the phenomenon of cavitation.
Phenomenon of cavitation are highly detrimental for equipment that is “sensitive” to such phenomenon because they generate mechanical damage to the equipment, degradation in the efficiency, noise, and, in certain circumstances, introduction of gas bubbles, which can be problematic for the equipment.
There therefore exists a genuine need for a grey-water management system that offers good energy efficiency, compactness, and low weight, that requires only low maintenance, and that is insensitive to the phenomenon of cavitation that can appear as a function of flight conditions, in particular.
In addition, it also appears that the pumps used in prior art grey-water management systems are more sensitive to pollution in the grey water. In the application in question, relating in particular to managing grey water in an aircraft, such prior art pumps suffer from problems of blocking or clogging when the grey water to be pumped is too dirty or contains too many foreign bodies and/or too much organic matter. Such pumps are too sensitive to the size of the waste or foreign bodies present in the grey water to be pumped.